During the broadband and mobile development of networks, the 3rd Generation Partnership Program (3rd Generation Partnership Program, 3GPP for short) organizations separately set forth a long term evolution (Long Term Evolution, LTE for short) scheme, that is, an evolved universal mobile telecommunication system (UMTS) territorial radio access network (Evolved Universal Mobile Telecommunication System Territorial Radio Access Network, E-UTRAN), in a mobile access network, and set forth a system architecture evolution (System Architecture Evolution, SAE for short) scheme, that is, an evolved packet core (Evolved Packet Core, EPC for short), in a mobile core network. The E-UTRAN and the EPC form an evolved packet system (Evolved Packet System, EPS for short). In addition to accessing the EPC through the E-UTRAN, a user equipment (User Equipment, UE for short) can also access the EPC through a universal mobile telecommunication system territorial radio access network (Universal Mobile Telecommunication System Territorial Radio Access Network, UTRAN for short) or a global system for mobile communications (Global System for Mobile Communications, GSM for short)/enhanced data rate for GSM evolution (Enhanced Data rate for GSM Evolution, EDGE for short) radio access network (GSM EDGE Radio Access Network, GERAN for short).
Idle mode signaling reduction (Idle mode Signaling Reduction, ISR for short) refers to a mechanism for reducing signaling interaction that is provided when a UE in idle mode reselects a radio access network. The ISR may include two states, that is, an activation state and a deactivation state. A situation where a UE performs reselection between an E-UTRAN and a UTRAN/GERAN is taken as an example. In an ISR activation scenario, the UE needs to be registered with both a mobility management network element, that is, a mobility management entity (Mobility Management Entity, MME for short) in the E-UTRAN and a mobility management network element, that is, a serving general packet radio service (General Packet Radio Service, GPRS for short) supporting node (Serving GPRS Supporting Node, SGSN for short) in the UTRAN/GERAN. In the ISR activation scenario, a serving gateway (Serving GateWay, SGW for short) reserves both connection information of the MME and connection information of the SGSN, for example, a full qualified tunnel endpoint identifier (Full Qualified TEID, F-TEID for short) of the MME/SGSN or an IP address of the MME/SGSN. The MME and the SGSN save the connection information of each other, that is, the MME saves the connection information of the SGSN, and the SGSN saves the connection information of the MME. That the SGW saves both the connection information of the MME and the connection information of the SGSN means ISR activation for the SGW; and that the MME and the SGSN save the connection information of each other means ISR activation for the MME and the SGSN.
In the ISR activation scenario, when the SGW receives downlink user plane data or downlink control plane data of the UE, according to the saved connection information of the MME and connection information of the SGSN, the SGW triggers the corresponding MME and SGSN to page the UE. Therefore, regardless of whether the UE currently resides in the E-UTRAN or the UTRAN/GERAN, the UE can make a response to a paging message of a corresponding network in the network where the UE resides (that is, a called-related service of the UE is reachable).
However, in the ISR activation scenario, if an SGW fails, for example, an SGW failure with restart (SGW failure with Restart, also referred to as reset) or an SGW failure without Restart (SGW failure without Restart), a service of the user equipment that the SGW serves before the SGW fails is interrupted, and service experience of the user equipment is influenced.